Fluid machine

ABSTRACT

A sub-compressor ( 23 ) is provided between a compressor ( 22 ) and a power-recovery device ( 24 ). A refrigerant after preliminarily being compressed by the sub-compressor ( 23 ) is allowed to flow into the compressor ( 22 ). Since the sub-compressor ( 23 ) and the power-recovery device ( 24 ) have approximately the same temperature, heat transfer hardly occur therebetween. Heat transfer occurs between the compressor ( 22 ) at high temperature and the sub-compressor ( 23 ) at low temperature. However, even if the heat from the compressor ( 22 ) heats the refrigerant in the sub-compressor ( 23 ), the refrigerant discharged from the sub-compressor ( 23 ) is delivered to the compressor ( 22 ), and thus the temperature of the sub-compressor ( 23 ) scarcely increases.

TECHNICAL FIELD

The present invention relates to a fluid machine to be used for a power-recovery type refrigeration cycle apparatus integrally including a compressor and a power-recovery device.

BACKGROUND ART

Conventionally, a so-called power-recovery type refrigeration cycle apparatus has been known in which an expander recovers, as kinetic energy, pressure energy that generates when a refrigerant expands and the recovered energy is used as a part of energy for driving a compressor (see, for example, the Patent literature 1).

FIG. 10 is a vertical sectional view showing a conventional fluid machine 10 integrally including a compressor and an expander. As shown in FIG. 10, the conventional fluid machine 10 includes a compressor 1, a rotation motor 7 and an expander 3 disposed in a closed casing 8 from the top in this order and coupled by a shared shaft 6.

FIG. 11 is a schematic diagram showing a power-recovery type refrigeration cycle apparatus 300 using the conventional fluid machine 10. As shown in FIG. 11, the conventional power-recovery type refrigeration cycle apparatus 300 includes the fluid machine 10, a first heat exchanger 2, a second heat exchanger 4, and refrigerant pipes 5 that connect the compressor 1, the first heat exchanger 2, the expander 3 and the second heat exchanger 4 in this order.

In the conventional power-recovery type refrigeration cycle apparatus 300, a refrigerant at low pressure is compressed by the compressor 1 to have a high temperature and high pressure. The heat is transferred by radiation, and thereby the refrigerant is cooled in the first heat exchanger 2. The refrigerant that has been allowed to have an intermediate temperature and high pressure in the first heat exchanger 2 expands in the expander 3 to have a low temperature and low pressure, and evaporates in the second heat exchanger 4 by absorbing heat. The refrigerant that has been allowed to have an intermediate temperature and low pressure in the second heat exchanger 4 returns to the compressor 1 again, and repeats the above-mentioned cycle. The expander 3 changes pressure energy that generates when the refrigerant expands into energy for driving the compressor 1 via the shaft 6 together with the rotation motor 7.

CITATION LIST Patent Literature

Patent literature 1: WO 2007/000854 A1

SUMMARY OF INVENTION Technical Problem

In the above-mentioned conventional fluid machine 10, however, the compressor 1 and the expander 3 are disposed adjacently in the closed casing 8, and therefore heat transfer occurs between the compressor 1 at high temperature and the expander 3 at low temperature. As a result, the heat exchange amounts of the first heat exchanger 2 and the second heat exchanger 4 decrease, which causes a problem that the COP (Coefficient of Performance) of the power-recovery type refrigeration cycle apparatus 300 decreases.

In response to this, the present invention has been accomplished, and it is therefore an object of the present invention sharply to reduce the heat transfer from a compressor to a power-recovery device so as to prevent the decrease in the COP of a power-recovery type refrigeration cycle apparatus.

Solution to Problem

In order to solve the above-mentioned problem, the fluid machine of the present invention includes: a closed casing; a rotation motor disposed in the closed casing and including a stator and a rotor; a compressor disposed in the closed casing for compressing refrigerant and discharging it into the closed casing; a power-recovery device disposed in the closed casing for recovering power from the refrigerant by suctioning and discharging the refrigerant; a shaft extending vertically shared by the rotation motor, the compressor and the power-recovery device; and a sub-compressor disposed between the compressor and the power-recovery device for raising the pressure of the refrigerant and delivering the refrigerant to the compressor with the rotation of the shaft.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the fluid machine of the present invention, the sub-compressor is provided between the compressor and the power-recovery device. Since the sub-compressor with a slight increase in temperature and the power-recovery device at low temperature have approximately the same temperature, heat transfer hardly occurs between the sub-compressor and the power-recovery device. Further, although heat transfer occurs between the compressor at high temperature and the sub-compressor at low temperature, the temperature increase in the sub-compressor hardly occurs. This is because, even if the heat from the compressor heats the refrigerant to be compressed in the sub-compressor, the refrigerant discharged from the sub-compressor is delivered to the compressor. Moreover, the heat conducted from the compressor to the sub-compressor is returned to the compressor again by the refrigerant, which means that the heat only circulates in the compression process.

Accordingly, in a power-recovery type refrigeration cycle apparatus using the fluid machine of the present invention, it is possible sharply to reduce heat transfer from the compressor at high temperature to the power-recovery device at low temperature, so as to improve the COP of the power-recovery type refrigeration cycle apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing a fluid machine according to Embodiment 1 of the present invention.

FIG. 2A is a horizontal sectional view showing a sub-compressor taken along the line IIA-IIA of FIG. 1, FIG. 2B is a horizontal sectional view showing an expander taken along the line IIB-IIB of FIG. 1, and FIG. 2C is a horizontal sectional view showing the expander taken along the line IIC-IIC of FIG. 1.

FIG. 3 is a schematic diagram showing a power-recovery type refrigeration cycle apparatus using the fluid machine shown in FIG. 1.

FIG. 4 is a Mollier diagram of the refrigeration cycle apparatus shown in FIG. 3.

FIG. 5 is a vertical sectional view showing a fluid machine according to Embodiment 2 of the present invention.

FIG. 6 is a horizontal sectional view showing a fluid pressure motor taken along the line VI-VI of FIG. 5.

FIG. 7 is a PV diagram of the expander in Embodiment 1 of the present invention and a fluid pressure motor in Embodiment 2 of the present invention.

FIG. 8 is a vertical sectional view showing a fluid machine of Modified Example 1.

FIG. 9A is a schematic diagram of a fluid machine of Modified Example 2, and FIG. 9B is a schematic diagram of a fluid machine of Modified Example 3.

FIG. 10 is a vertical sectional view showing a conventional fluid machine.

FIG. 11 is a schematic diagram of a power-recovery type refrigeration cycle apparatus using the fluid machine shown in FIG. 10.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described in detail with reference to the drawings. In the embodiments of the present invention, an example in which the present invention is applied to a heat pump using carbon dioxide as refrigerant is described. The components identical to those in the conventional example are indicated with the same numerals, and the descriptions thereof are omitted.

Embodiment 1 Configuration of Fluid Machine 21

FIG. 1 is a vertical sectional view showing a fluid machine 21 according to Embodiment 1 of the present invention. FIG. 2A is a horizontal sectional view showing a sub-compressor 23 taken along the line IIA-IIA of FIG. 1, FIG. 2B is a horizontal sectional view showing an expander 24 as a power-recovery device taken along the line IIB-IIB of FIG. 1, and FIG. 2C is a horizontal sectional view showing the expander 24 taken along the line IIC-IIC of FIG. 1.

As shown in FIG. 1, the fluid machine 21 of Embodiment 1 includes a longitudinal cylindrical closed casing 8. Inside the closed casing 8, a scroll compressor 22, a rotation motor 7 including a stator 7 a and a rotor 7 b, a rotary sub-compressor 23 and two-stage rotary expander 24 are disposed from the top in this order. The compressor 22, the rotation motor 7, the sub-compressor 23 and the expander 24 are uniaxially coupled by a shaft 6 extending vertically. In other words, the compressor 22, the rotation motor 7, the sub-compressor 23 and the expander 24 share the shaft 6.

An oil pool 34 is formed in the bottom of the closed casing 8. In this Embodiment 1, the oil level 34 a of the oil pool 34 is higher than the after-mentioned oil pump 35 and lower than the rotation motor 7, and the sub-compressor 23 and the expander 24 are immersed in the oil pool 34. In the upper part of the closed casing 8, a discharge pipe 47 is provided for discharging, to the outside of the closed casing 8, the refrigerant that has been discharged from the compressor 22 into the closed casing 8. In the lateral part of the closed casing 8, a suction pipe 46 for the compressor 22, a discharge pipe 59 and a suction pipe 63 for the sub-compressor 23, and a suction pipe 81 and a discharge pipe 83 for the expander 24 each are provided through the closed casing 8. The suction pipe 46 for the compressor 22 and the discharge pipe 59 for the sub-compressor 23 are connected by a refrigerant pipe 29.

The shaft 6 is formed by integrally connecting a main shaft 31 and a secondary shaft 32 by a joint 33. The main shaft 31 is supported rotatably by an upper bearing member 44 and a lower bearing member 36, and equipped with an eccentric portion 31 b at its upper end portion. Inside the main shaft 31, an oil supply passage 31 a is formed, and this oil supply passage 31 a connects with an oil pump 35 provided above the sub-compressor 23. The secondary shaft 32 is supported rotatably by an upper bearing member 54 and a lower bearing member 78, and equipped with eccentric portions 32 a, 32 b and 32 c therebetween. Inside the secondary shaft 32, an oil supply passage 32 d opening into the oil pool 34 at the lower end surface of the secondary shaft 32 is formed.

The scroll compressor 22 includes the main shaft 31 shared with the rotation motor 7, a stationary scroll 41, a orbiting scroll 42, an Oldham ring 43 and a muffler 45.

The stationary scroll 41 is fixed to the inner surface of the closed casing 8, and provided with the muffler 45 on its upper surface. The upper bearing member 44 is fixed to the lower surface of the stationary scroll 41 so as to sandwich the orbiting scroll 42 therebetween. A spiral-shaped lap 41 a is formed on the lower surface of the stationary scroll 41, and a discharge port 41 c is formed at the center thereof. Similarly, the spiral-shaped lap 42 a is formed on the upper surface of the orbiting scroll 42. The orbiting scroll 42 is disposed opposite to the stationary scroll 41 so that the lap 42 a meshes with the lap 41 a of the stationary scroll 41. Thereby, a crescent-shaped working chamber 48 is formed between the lap 41 a and the lap 42 a. The lower surface of the orbiting scroll 42 is fitted to the eccentric portion 31 b of the main shaft 31, and the Oldham ring 43 for restraining the rotational motion of the orbiting scroll 42 is disposed between the periphery of the orbiting scroll 42 and the upper bearing member 44.

With the orbiting motion of the orbiting scroll 42 that accompanies the rotation of the main shaft 31, the crescent-shaped working chamber 48 reduces its volume while moving from the outside to the inside. Thereby, the refrigerant suctioned through the suction pipe 46 is compressed. The compressed refrigerant is discharged to the internal space of the closed casing 8 through the discharge port 41 c of the stationary scroll 41, the internal space of the muffler 45 and a flow path 49 that is provided in the periphery of the stationary scroll 41 and upper bearing member 44 and penetrates them.

The refrigerant discharged into the above-mentioned internal space flows down to the lower side of the rotation motor 7 with lubricating oil being mixed therein. Then, after being separated from oil by gravity or centrifugal force, the refrigerant rises in the internal space of the closed casing 8 and is discharged through the discharge pipe 47 to the outside.

In this embodiment, a trochoid pump is employed as an oil pump 35. The oil in the oil pool 34 is supplied by the oil pump 35 to the compressor 22 through the oil supply passage 31 a in the main shaft 31, and lubricates sliding portions of the compressor 22 and seals gaps thereof. Thereafter, the oil discharged from the compressor 22 drops into the above-mentioned internal space, and flows down to the lower side of the rotation motor 7 together with the refrigerant. Then, after being separated from the refrigerant by gravity or centrifugal force, the oil returns to the oil pool 34.

Above the oil pump 35, the substantially disc-shaped lower bearing member 36 having the same diameter as the internal diameter of the closed casing 8 is fixed to the inner surface of the closed casing 8. The oil pump 35 is fixed to the lower surface of the lower bearing member 36. The lower bearing member 36 is provided with through openings 36 a for oil circulation at an appropriate position.

Below the joint 33, the substantially disc-shaped upper bearing member 54 having the same diameter as the internal diameter of the closed casing 8 is fixed to the inner surface of the closed casing 8. In the periphery of the upper bearing member 54, a connection path 54 a is provided penetrating the upper bearing member 54. This connection path 54 a allows oil to flow between the upper side and the lower side of the oil pool 34 that are partitioned by the upper bearing member 54, and the amount of oil is adjusted automatically therebetween. The lower bearing member 78 is fixed to the lower surface of the upper bearing member 54, so as to sandwich the sub-compressor 23 and the expander 24 therebetween.

The rotary sub-compressor 23 includes, as shown in FIG. 2 A, the secondary shaft 32, a cylinder 51, a piston 52, a vane 53, a spring 62 and a discharge valve 61 (see FIG. 1). It should be noted that the discharge valve 61 is not an essential component. In the case where the discharge valve 61 is provided, as is the case of this embodiment, refrigerant is compressed inside the sub-compressor 23, which is described later. In the case where the discharge valve 61 is not provided, the sub-compressor 23 forcedly discharges the refrigerant and thereby the refrigerant is compressed outside the sub-compressor 23. Thus, in either of the cases, the sub-compressor 23 raises the pressure of the refrigerant.

The piston 52 is disposed in the cylinder 51. The piston 52 is fitted to the eccentric portion 32 a of the secondary shaft 32, and eccentrically rotates with the rotation of the secondary shaft 32. Over the cylinder 51 and the piston 52, the upper bearing member 54 is provided in contact with their upper end surfaces. Under the cylinder 51 and the piston 52, a first intermediate plate 55 is provided in contact with their lower end surfaces. Thereby, a crescent-shaped space 57 is formed inside the sub-compressor 23.

The cylinder 51 is provided with a vane groove 51 a into which a vane 53 is inserted. On the back of the vane 53, the spring 62 is provided so that the tip of the vane 53 touches the outer periphery surface of the piston 52. Thereby, the above-mentioned crescent-shaped space 57 is partitioned into a suction working chamber 57 a and a discharge working chamber 57 b.

In Embodiment 1, a disc-shaped discharge cover 56 having a slightly smaller diameter than the upper bearing member 54 is provided above the upper bearing member 54. Thereby, a discharge space 56 a extending over the sub-compressor 23 is formed between the sub-compressor 23 and the oil pump 35. Specifically, a circular recess is provided on the upper surface of the upper bearing member 54, forming a circle around the secondary shaft 32. This recess is closed with the discharge cover 56, thereby forming the discharge space 56 a. The discharge space 56 a is filled with the refrigerant immediately after being discharged from the sub-compressor 23. The discharge space 56 a is in connection with the discharge pipe 59, and the refrigerant once discharged into the discharge space 56 a is discharged through the discharge pipe 59 to the outside. It is desirable that the discharge space 56 a occupies an area as large as possible in the radial cross-sectional area of the closed casing 8, the reason for which is described later.

A suction port 58 is formed in the cylinder 51 and the upper bearing member 54 reaching from the suction pipe 63 to the suction working chamber 57 a. Through the suction port 58, the refrigerant is suctioned from the suction pipe 63 that is connected to the cylinder 51 into the suction working chamber 57 a. Further, a discharge port 60 is formed in the upper bearing member 54 penetrating the upper bearing member 54. Through the discharge port 60, the refrigerant is discharged from the discharge working chamber 57 b to the discharge space 56 a. In the upper part of the discharge port 60, the discharge valve 61 for setting the pressure is provided. The discharge valve 61 controls the flow of the refrigerant.

When the piston 52 eccentrically rotates with the rotation of the secondary shaft 32, the suction port 58 connects with the suction working chamber 57 a, and thereby the refrigerant is suctioned through the suction pipe 63 with an accompanying increase in the volume of the suction working chamber 57 a. Upon the completion of one rotation by the secondary shaft 32, the suction working chamber 57 a shifts to the discharge working chamber 57 b to connect with the discharge port 60. With further rotation of the secondary shaft 32, the volume of the discharge working chamber 57 b is reduced, and thereby the refrigerant is compressed. If the pressure of the compressed refrigerant reaches a particular pressure, the discharge valve 61 deforms causing the discharge port 60 to open, so that the refrigerant flows into the discharge space 56 a. This allows the refrigerant filling the discharge space 56 a to be pushed out into the discharge pipe 59.

For positive recovery, by the refrigerant, of the heat moving from the side of the compressor 22 to the side of the expander 24, the discharge space 56 a plays a role in putting the refrigerant in contact over a large area with the heat conduction members (the discharge cover 56 and the upper bearing member 54 in this embodiment) therebetween. By thus enlarging the area over which the refrigerant is in contact with the heat conduction members, it is possible efficiently to recover the heat moving from the side of the compressor 22 to the side of the expander 24 using the refrigerant passing through the discharge space 56 a. In addition, due to providing this discharge space 56 a, an excellent heat-insulating effect can be achieved between the compressor 22 and the sub-compressor 23.

In view of enhancing the heat-conduction efficiency, it is preferable that the flow of refrigerant toward the discharge pipe 56 be formed entirely inside the discharge space 56 a. In view of this, the discharge pipe 59 and the discharge port 60 are preferably located as far apart as possible. For achieving this, it is preferable that the discharge pipe 59 and the discharge port 60 be oppositely located across the secondary shaft 32.

Meanwhile, the closed casing 8 is in contact with the compressor 22 and the stator 7 a of the rotation motor 7. Therefore, the closed casing 8 serves as a heat conduction path, so that heat is conducted to the refrigerant flowing in the suction pipe 81 and the discharge pipe 83 for the expander 24, or heat is conducted to the oil around the expander 24. In order to prevent this, the upper bearing member 54 in contact with the closed casing 8 and the discharge cover 56 touching there may be composed of a material having a higher heat conductivity than the closed casing 8, so that the heat to be conducted through the closed casing 8 is positively conducted to the discharge space 56 a. Generally, the closed casing 8 is composed of iron materials such as carbon steel and cast iron. In this case, for example, copper materials such as brass or aluminum materials such as duralumin can be used as a material for the upper bearing member 54 and the discharge cover 56. Thus, the heat-recovery effect by the refrigerant in the discharge space 56 a can be enhanced further.

The two-stage rotary expander 24 includes, as shown in FIG. 2B and FIG. 2C, the secondary shaft 32 shared with the sub-compressor 23, a first cylinder 71, a second cylinder 72, a first piston 73, a second piston 74, a first vane 75, a second vane 76, a second intermediate plate 77, a first spring 85, and a second spring 86.

The first piston 73 and the second piston 74 are disposed respectively inside the first cylinder 71 and the second cylinder 72. The first piston 73 and the second piston 74 are fitted respectively to the eccentric portions 32 b and 32 c of the secondary shaft 32, and eccentrically rotate with the rotation of the secondary shaft 32. Over the first cylinder 71 and the first piston 73, the first intermediate plate 55 is provided in contact with their upper end surfaces. Under the second cylinder 72 and the second piston 74, the lower bearing member 78 is provided in contact with their lower end surfaces. Between the first cylinder 71 with the first piston 73 and the second cylinder 72 with the second piston 74, the second intermediate plate 77 is provided in contact with the lower end surfaces of the first cylinder 71 and the first piston 73, and the upper end surfaces of the second cylinder 72 and the second piston 74. Thereby, a first crescent-shaped space 79 and a second crescent-shaped space 80 are formed inside the expander 24 so as to interpose the second intermediate plate 77 therebetween.

Further, the first cylinder 71 and the second cylinder 72 are provided respectively with a first vane groove 71 a and a second vane groove 72 a, into which a first vane 75 and a second vane 76 are inserted respectively. On the back of the first vane 75 and the second vane 76, the first spring 85 and the second spring 86 are provided respectively so that the tips of the first vane 75 and the second vane 76 respectively touch the outer periphery surfaces of the first piston 73 and the second piston 74. Thereby, the above-mentioned first crescent-shaped space 79 and second crescent-shaped space 80 are partitioned respectively into a first suction working chamber 79 a and a first discharge working chamber 79 b, and a second suction working chamber 80 a and a second discharge working chamber 80 b. In this Embodiment 1, the volume of the second space 80, that is, the total volume of the second suction working chamber 80 a and the second discharge working chamber 80 b is designed to exceed the volume of the first space 79, that is, the total volume of the first suction working chamber 79 a and the first discharge working chamber 79 b. The ratio of these volumes corresponds to the increase in the specific volume of the refrigerant caused by the expansion.

A suction port 82 reaching from the suction pipe 81 to the first suction working chamber 79 a is formed in the first intermediate plate 55 and the first cylinder 71. The refrigerant is suctioned from the suction pipe 81 connected to the first intermediate plate 55 into the first suction working chamber 79 a. A discharge port 84 reaching from the second discharge working chamber 80 b to the discharge pipe 83 is formed in the second cylinder 72 and the lower bearing member 78. The refrigerant is discharged from the second discharge working chamber 80 b into the discharge pipe 83 connected to the lower bearing member 78. In the second intermediate plate 77, a connection port 77 a connecting between the first discharge working chamber 79 b and the second suction working chamber 80 a is formed, which constitute an expansion chamber.

When the first piston 73 eccentrically rotates with the rotation of the secondary shaft 32, the suction port 82 connects with the first suction working chamber 79 a and thereby the refrigerant is suctioned through the suction pipe 81 with an accompanying increase in the volume of the first suction working chamber 79 a. Upon the completion of one rotation by the secondary shaft 32, the first suction working chamber 79 a shifts to the first discharge working chamber 79 b to connect with the second suction working chamber 80 a via the connection port 77 a. With further rotation of the secondary shaft 32, the volume of the first discharge working chamber 79 b is reduced and the volume of the second suction working chamber 80 a connecting therewith via the connection port 77 a is increased, and thereby the refrigerant expands. Thereafter, upon the completion of one more rotation by the secondary shaft 32, the first discharge working chamber 79 b disappears, the connection port 77 a is closed, and the second suction working chamber 80 a shifts to the second discharge working chamber 80 b. With further rotation of the secondary shaft 32, the volume of the second discharge working chamber 80 b is reduced, and the refrigerant is discharged from the discharge pipe 83 to the outside via the discharge port 84.

<Schematic Configuration of Power-Recovery Type Refrigeration Cycle Apparatus 100>

FIG. 3 is a schematic diagram showing a power-recovery type refrigeration cycle apparatus 100 using the fluid machine 21 according to Embodiment 1 of the present invention. As shown in FIG. 3, the power-recovery type refrigeration cycle apparatus 100 according to this Embodiment 1 includes the fluid machine 21, the first heat exchanger 2, the second heat exchanger 4, and the refrigerant pipes 29. The refrigerant pipes 29 connect each component, that is, the compressor 22, the first heat exchanger 2, the expander 24, the second heat exchanger 4, and the sub-compressor 23, in this order.

In this Embodiment 1, an example is described in which the refrigerant pipes 29 are filled with refrigerant (specifically, carbon dioxide) that is brought into a supercritical state at a high pressure side (zone from the compressor 22 through the first heat exchanger 2 to the expander 24). It should be noted that, in the present invention, the refrigerant is not limited to the one that is brought into a supercritical state at a high pressure side. It may be one that is not brought into a supercritical state at a high pressure side (such as fluorocarbon refrigerant).

The refrigerant at intermediate temperature and low pressure is compressed to have a high temperature and high pressure in the compressor 22, and thereafter cooled in the first heat exchanger 2 by heat-exchanging with the outside, so as to have an intermediate temperature and high pressure. Then, the refrigerant expands from intermediate temperature and high pressure to low temperature and low pressure in the expander 24, and thereafter heated in the second heat exchanger 4 by heat-exchanging with the outside, so as to have an intermediate temperature and low pressure. Thereafter, the refrigerant is compressed from intermediate temperature and low pressure to intermediate pressure in the sub-compressor 23, and returns to the compressor 22 again. The expander 24 changes expansion pressure energy generated when the refrigerant expands into energy for driving the compressor 22 and the sub-compressor 23 via the shaft 6 together with the rotation motor 7.

<Temperature Distribution in Fluid Machine 21>

FIG. 4 is a Mollier diagram of the power-recovery type refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention. In FIG. 4, the line from point A to point B indicates the compression process by the sub-compressor 23, the line from point B to point C indicates the compression process by the main compressor 22, the line from point C to point D indicates the heat radiation process by the first heat exchanger 2, the line from point D to point E indicates the expansion process by the expander 24, and the line from point E to point A indicates the evaporation process by the second heat exchanger 4. The amount of work, the amount of heat exchange, or the amount of power recovery in each process can be calculated from the difference of the enthalpy between the two points.

In FIG. 4, h_(A) indicates the enthalpy at the inlet of the sub-compressor 23, h_(B) indicates the enthalpy at the outlet of the sub-compressor 23, h_(C) indicates the enthalpy at the outlet of the compressor 22, h_(D) indicates the enthalpy at the inlet of the expander 24 and h_(E) indicates the enthalpy at the outlet of the expander 24.

Further, in FIG. 4, the dashed line T_(D) indicates the temperature of point D representing the status of the suction side of the expander 24, the dashed line T_(E) indicates the temperature of point E representing the status of the discharge side of the expander 24, the dashed line T_(C) indicates the temperature of point C representing the status of the discharge side of the compressor 22, each of which defines an isotherm at that temperature.

As seen from FIG. 4, the temperatures of the dashed line T_(D) and the dashed line T_(E) are relatively close, and are lower compared to the temperature of the dashed line T_(C). Specifically, for example, in the case of a heat pump to be used for a water heater, the dashed line T_(C) is about 100° C., the dashed line T_(D) is about 25° C., and the dashed line T_(E) is about 5° C. The temperature of point A that is the temperature of the inlet side of the sub-compressor 23 is just slightly higher than the temperature of the dashed line T_(E). This temperature difference is defined as “superheat degree” in the refrigeration cycle apparatus 100 according to Embodiment 1. A normal superheat degree is about 5° C., although it depends on the operational conditions of the refrigeration cycle apparatus. Generally, in view of reducing the compression work of the compressor, the lower the superheat degree is, the more desirable it is.

Further, it is understood that the temperature of point B that is the temperature of the outlet side of the sub-compressor 23 is relatively close to the temperature of the dashed line T_(D). Particularly, in the case where the compression ratio of the sub-compressor 23, that is, the ratio of the suction volume of the sub-compressor 23 with respect to the suction volume of the compressor 22 is 1.2, the temperature increase from point A to point B can be kept at about 20° C., which is approximately the same as the temperature difference between the dashed line T_(D) and the dashed line T_(E). Further, considering that the temperature of point A is approximately the same as the temperature of the dashed line T_(E), it is an indicator of reducing the temperature difference between the sub-compressor 23 and the expander 24 to keep the compression ratio of the sub-compressor 23 to at 1.2 or less.

It should be noted that the compression ratio r of the sub-compressor 23 can be calculated from the following formula (Formula 1) using the suction volume V′ of the sub-compressor 23, the suction volume V of the compressor 22 and the adiabatic index κ of the refrigerant. Practically, since the adiabatic index κ of the refrigerant is about 1.1 to 1.2, approximation of κ≈1 is not significant and thus the value obtained by Formula 1 approximately corresponds to the ratio of the suction volume V′ of the sub-compressor 23 to the suction volume V of the compressor 22.

r=(V′/V)^(κ)  Formula 1

<Heat Flow Inside Fluid Machine 21>

The refrigerant discharged from the compressor 22 is, as mentioned above, once discharged into the internal space of the closed casing 8, and therefore the refrigerant above the oil level 34 a of the oil pool 34 in the closed casing 8 has a high temperature indicated by point C (about 100° C.). Thereby, the portion of the oil pool 34 near the oil level 34 a is in contact with the refrigerant at high temperature remaining in the internal space of the closed casing 8 and is covered by the oil at high temperature that has separated from the refrigerant after lubricating the compressor 22 at high temperature and dropped therein. Accordingly, its temperature is high.

Meanwhile, the sub-compressor 23 disposed in the oil pool 34 has a temperature between point A and point B, and the expander 24 disposed further therebelow has a temperature between point D and point E. In the case where the compression ratio of the sub-compressor 23 is 1.2 or less, each temperature of point D, point E, point A and point B is relatively close to each other within the range of about 5° C. to 25° C., and is considerably lower compared to the temperature of point C, as already mentioned above. This reduces the temperature of the neighborhood of the sub-compressor 23 in the oil pool 34, which is under the influence of the internal temperature of the sub-compressor 23. Particularly, in this Embodiment 1, the discharge space 56 a covering over the sub-compressor 23 is provided, and therefore the oil in contact with the discharge cover 56 in the oil pool 34 further is cooled to a temperature close to the temperature of point B corresponding to the temperature of the refrigerant in the discharge space 56 a. Further, the oil remaining below the sub-compressor 23 in the oil pool 34 has approximately the same temperature as the neighborhood of the sub-compressor 23, because the temperatures of the sub-compressor 23 and the expander 24 are relatively close.

Thus, temperature stratification from the temperature of point C to the temperature of point B is formed between the oil level 34 a and the discharge cover 56 over the sub-compressor 23 in the oil pool 34, and a temperature layer at almost constant temperature in which no heat transfer occurs is formed between the sub-compressor 23 and the expander 24.

Heat transfer occurs between the compressor 22 and the sub-compressor 23 via the above-mentioned temperature stratification. In other words, the refrigerant at high temperature discharged from the compressor 22 into the closed casing 8 reduces the temperature by radiating heat to the oil pool 34. The refrigerant at reduced temperature rises in the closed casing 8 and is discharged through the discharge pipe 47 to the first heat exchanger 2. Thereafter, the refrigerant that has passed through the expander 24 and the second heat exchanger 4 is suctioned into the sub-compressor 23. In the sub-compressor 23, the refrigerant is compressed, and it absorbs heat from the oil pool 34, resulting in an increase in its temperature. The refrigerant at increased temperature is discharged from the discharge pipe 59 into the refrigerant pipe 29, and immediately suctioned from the suction pipe 46 into the compressor 22. In the compressor 22, the refrigerant is suctioned into the compressor with the heat absorbed from the oil pool 34, and therefore the temperature of the refrigerant after the compression is more increased compared to the case without the heat absorbed from the oil pool 34. The temperature increase in the compressor 22 is cancelled out by the heat transfer via the refrigerant from the compressor 22 to the sub-compressor 23 via the temperature stratification.

As seen from this, heat circulates between the compressor 22 and the sub-compressor 23, due to the temperature stratification in the oil pool 34 and the direct flow of the refrigerant from the sub-compressor 23 to the compressor 22. Accordingly, in spite that there is a large temperature difference between the compressor 22 and the sub-compressor 23, it is possible to achieve a state in which substantially no heat transfer occurs.

<Effects of Configuration of Fluid Machine 21>

As described above, in the fluid machine 21 in this Embodiment 1, the sub-compressor 23 is disposed between the compressor 23 and the expander 24, and thereby substantially no heat transfer from the compressor 22 to the sub-compressor 23 occurs due to the circulation of heat. At the same time, heat transfer from the sub-compressor 23 to the expander 24 does not occur because their temperatures are approximately the same. Accordingly, heat transfer from the compressor 22 to the expander 24 can be suppressed. Particularly, in the case where the compressor 22, the sub-compressor 23 and the expander 24 are aligned in the vertical direction inside the closed casing 8, the heat transfer between each component mentioned above becomes more significant. This is because the oil pump 35 supplies oil from the oil pool 34 in the bottom to the compressor 22 at the top, thus causing the circulation of the oil in the vertical direction. Even in such a case, the amount of heat exchange between the first heat exchanger 2 and the second heat exchanger 4 can be ensured while achieving the power-recovery effect by the expander 24. Thus, an efficient heat pump is feasible.

Further, the compressor 22 is disposed above the expander 24 with the sub-compressor 23 being disposed therebetween, and therefore the temperature is high in the upper side and the temperature is low in the lower side inside the closed casing 8. Thus, heat transfer caused by natural convection can be prevented. Accordingly, the effect of suppressing the heat transfer using the sub-compressor 23 is enhanced more significantly.

Further, since the sub-compressor 23 is disposed in the oil pool 34 in the bottom of the closed casing 8, the sub-compressor 23 can absorb the heat efficiently from the compressor 22 via the oil that has a higher heat conductivity than the refrigerant. Accordingly, the effect of suppressing the heat transfer using the sub-compressor 23 is enhanced more significantly.

Further, by disposing the compressor 22 above the rotation motor 7, a great distance can be obtained between the compressor 22 and the sub-compressor 23, and therefore the effect of suppressing the heat transfer using the sub-compressor 23 is enhanced more significantly.

In addition, since the oil pump 35 that supplies oil for lubrication to the compressor 22 is disposed above the sub-compressor 23, the oil at high temperature that lubricates the compressor 22 is allowed to circulate above the sub-compressor 23. Accordingly, forced convection that may cause heat transfer from the compressor 22 to the expander 24 can be prevented, and therefore the effect of suppressing the heat transfer using the sub-compressor 23 is enhanced more significantly.

Further, since the compressor 22 is a scroll type, even if disposed above the rotation motor 7, the compressor 22 is easy to lubricate with oil. Therefore, it is possible to make the effect of suppressing the heat transfer and the reliability of the compressor 22 compatible.

Furthermore, the discharge space 56 a covering over the sub-compressor 23 is provided above the sub-compressor 23 and the covering ratio by the discharge space 56 a is high in the radial cross section of the closed casing 8, while being filled with the refrigerant discharged from the sub-compressor 23. Thereby, the refrigerant efficiently can absorb the heat conducting from the compressor 22 of the upper side to the lower side in the discharge space 56 a. Accordingly, compared to the case without the discharge space 56 a being disposed above the sub-compressor 23, the effect of suppressing the heat transfer is enhanced more significantly.

It is needless to say that advantageous effects can be achieved as long as the discharge space 56 a covers over at least a part of the sub-compressor 23, and a similar effect can be achieved, even if a suction space filled with the refrigerant immediately before being suctioned into the sub-compressor 23 is provided, instead of the discharge space 56 a. To provide the suction space between the sub-compressor 23 and the oil pump 35, the suction pipe 63 may be connected to the upper bearing member 56 as well as the discharge pipe 59 is connected to the cylinder 51.

Further, since the sub-compressor 23 is a one-stage rotary type and the expander 24 is a two-stage rotary type, that is, a rotary type is employed in either of them, the configuration of the cylinders of the sub-compressor 23 and the expander 24 can be as simple as in a three-stage rotary type. Thus, increases in size and cost of providing the sub-compressor 23 can be prevented. Further, the configuration in which the sub-compressor 23 is immersed into the oil pool 34 is facilitated.

In addition, since carbon dioxide is used as the refrigerant, the power-recovery effect by the expander 24 is enhanced, compared to the case of use of fluorocarbon. Moreover, even if the temperature of the refrigerant discharged from the compressor 22 is high and the amount of heat transfer from the compressor 22 to the expander 24 increases, the sub-compressor 23 can enhance the effect of suppressing the heat transfer more significantly.

Further, by keeping the compression ratio of the sub-compressor 23, that is, the ratio of the suction volume of the sub-compressor 23 with respect to the suction volume of the compressor 22 at 1.2 or less, the temperature of the sub-compressor 23 and the temperature of the expander 24 are allowed to be closer, thereby reducing the temperature difference almost completely. As a result, the effect of suppressing the heat transfer by the sub-compressor 23 is enhanced more significantly.

It is needless to say that even if the compression ratio of the sub-compressor 23 exceeds 1.2, it does not mean that the effect of suppressing the heat transfer by the sub-compressor 23 disappears, and whatever the compression ratio may be, the temperature of the sub-compressor 23 is lower than that of the compressor 22, and thus the effect of suppressing the heat transfer can be achieved.

Embodiment 2 <Configuration of Fluid Machine 121>

FIG. 5 is a vertical sectional view showing a fluid machine 121 according to Embodiment 2 of the present invention. FIG. 6 is a horizontal sectional view showing a fluid pressure motor taken along the line VI-VI of FIG. 5. The fluid machine 121 in Embodiment 2 of the present invention has the same configuration as in Embodiment 1, except that a rotary fluid pressure motor 124 is used instead of the expander 24 as a power-recovery device for recovering power from refrigerant by suctioning and discharging the refrigerant. Further, a power-recovery type refrigeration cycle apparatus 200 according to Embodiment 2 of the present invention also has the same configuration as in Embodiment 1. Accordingly, the configuration identical to that in Embodiment 1 is indicated with the same numeral, and the description thereof is omitted.

As shown in FIG. 5 and FIG. 6, in the fluid machine 121 in this Embodiment 2, the scroll compressor 22, the rotation motor 7 including the stator 7 a and the rotor 7 b, the rotary sub-compressor 23, and the rotary fluid pressure motor 124 are disposed in the closed casing 8 from the top in this order, and these are uniaxially coupled by the shaft 6.

The oil pool 34 is formed in the bottom of the closed casing 8. The oil level 34 a of the oil pool 34 in this Embodiment 2 is higher than the oil pump 35 in the same manner as in Embodiment 1, and the sub-compressor 23 and the fluid pressure motor 124 are immersed in the oil pool 34. In the upper part of the closed casing 8, the discharge pipe 47 for discharging, to the outside of the closed casing 8, the refrigerant that has been discharged from the compressor 22 into the closed casing 8 is provided. In the lateral part of the closed casing 8, the suction pipe 46 for the compressor 22, the discharge pipe 59 and the suction pipe 63 for the sub-compressor 23, and a suction pipe (not shown) and a discharge pipe 183 for the fluid pressure motor 124 each are provided through the closed casing 8. The suction pipe 46 for the compressor 22 and the discharge pipe 59 for the sub-compressor 23 are connected by the refrigerant pipes 29.

The shaft 6 is formed by integrally connecting the main shaft 31 and a secondary shaft 132 by a joint 33. The main shaft 31 is supported rotatably by the upper bearing member 44 and the lower bearing member 36, and equipped with the eccentric portion 31 b at its upper end portion. Inside the main shaft 31, the oil supply passage 31 a is formed, and this oil supply passage 31 a connects with the oil pump 35 provided at the lower portion of the main shaft 31. The secondary shaft 132 is supported rotatably by the upper bearing member 54 and the lower bearing member 178, and equipped with eccentric portions 132 a and 132 b therebetween. Inside the secondary shaft 132, an oil supply passage 132 d opening into the oil pool 34 at the lower end surface of the secondary shaft 132 is formed.

The rotary fluid pressure motor 124 includes the secondary shaft 132 shared with the sub-compressor 23, a cylinder 171, a piston 173, a vane 175 and a spring 162.

The piston 173 is disposed inside the cylinder 171. The piston 173 is fitted to the eccentric portion 132 b of the secondary shaft 132, and eccentrically rotates with the rotation of the secondary shaft 132. Over the cylinder 171 and the piston 173, the first intermediate plate 55 is provided in contact with their upper end surfaces. Under the cylinder 171 and the piston 173, the lower bearing member 178 is provided in contact with their lower end surfaces. Thereby, a crescent-shaped space 179 is formed inside the fluid pressure motor 124.

The cylinder 171 is provided with a vane groove 171 a into which a vane 175 is inserted. On the back of the vane 175, the spring 162 is provided so that the tip of the vane 175 touches the outer periphery surface of the piston 173. Thereby, the above-mentioned crescent-shaped space 179 is partitioned into a suction working chamber 179 a and a discharge working chamber 179 b.

In the fluid pressure motor 124 in this Embodiment 2, although the basic configuration of the rotary mechanism is the same as that of the sub-compressor 23, shapes of a suction port 182 and a discharge port 184 are different. Hereinafter, the suction port 182 and the discharge port 184 are described in detail.

The suction port 182 and the discharge port 184 are formed only in the lower bearing member 178. The suction port 182 and the discharge port 184 are formed so that when the piston 173 is positioned at the top dead center, a part of their contours each substantially overlap with the contour of the outer periphery surface of the piston 173. Thereby, the suction port 182 and the discharge port 184 are completely closed by the piston 173 at the moment that the piston 173 is positioned at the top dead center or in an extremely short period before and after the moment, and other than that, at least a part of them is open. Accordingly, except for the moment that the piston 173 is positioned at the top dead center, the suction working chamber 179 a connects with the suction port 182 and the discharge working chamber 179 b connects with the discharge port 184 at any time, while the vane 175 prevents the refrigerant from flowing directly from the suction port 182 to the discharge port 184. Then, torque is applied to the secondary shaft 132 due to the pressure difference between the suction working chamber 179 a at high pressure and the discharge working chamber 179 b at low pressure, and thus power is recovered. In this regard, the refrigerant reduces its pressure and expands at the time when the suction working chamber 179 a shifts to the discharge working chamber 179 b and the discharge working chamber 179 b connects with the discharge port 184.

<Action/Effect of Fluid Machine 121>

FIG. 7 is a PV diagram of the fluid pressure motor 124 in the present Embodiment 2 and the expander 24 in Embodiment 1.

As shown in FIG. 7, the expansion process of the expander 24 is indicated by the line from point D to point S to point E, and the recovery power thereof corresponds to the area of GDSEIH. If the pressure ratio of the refrigeration cycle does not match the expansion ratio of the expander 24, the loss from overexpansion corresponding to the area of EJK occurs. In contrast, there is no expansion process in the fluid pressure motor 124 and thus the recovery power thereof corresponds to the area of GDIH, which is lower than in the expander 24. However, in the case where carbon dioxide is used for the refrigerant, the recovery power in the expander 24 obtained from the expansion of the refrigerant corresponding to the area DSEI is very low, compared to the total recovery power in the expander 24. Further, if the loss from overexpansion occurs in the expander 24, the loss from overexpansion) offsets the recovery power, or exceeds the recovery power obtained from the expansion.

Accordingly, considering the various operational conditions for the refrigeration cycle, in the case of using the fluid pressure motor 124, it is possible to achieve a power recovery effect equivalent to that achieved using the expander 24, and the fluid pressure motor 124 has a very simple configuration compared to the expander 24. Further, the fluid pressure motor 124 can be formed integrally with the sub-compressor 23 having a simple configuration as if they were a two-stage rotary compressor, and thus while heat transfer suppression using the sub-compressor 23 is carried out, further reductions in cost and size can be achieved.

Modified Example

In the above-mentioned Embodiments, although examples using the scroll compressor 22 have been described, the present invention is not limited to the above-mentioned configurations. For example, as shown in FIG. 8, below the rotation motor 7, a rotary compressor 222, a rotary sub-compressor 223 and a rotary expander 224 may be disposed in the closed casing 8 from the top in this order and they may be integrated, which serves as a fluid machine 221.

Further, in the above-mentioned Embodiment, the compressor 22, the rotation motor 7, the sub-compressor 23 and the expander 24 (or the fluid pressure motor 124) are disposed in the closed casing 8 from the top in this order, however, the present invention is not limited to the above-mentioned configuration. For example, as shown in FIG. 9 A, the expander 24 (or the fluid pressure motor 124), the rotation motor 7, the sub-compressor 23 and the compressor 22 may be aligned from the top in this order. Alternatively, as shown in FIG. 9 B, the expander 24 (or the fluid pressure motor 124), the sub-compressor 23, the rotation motor 7 and the compressor 22 may be aligned from the top in this order.

INDUSTRIAL APPLICABILITY

The fluid machine of the present invention is useful for power-recovery type refrigeration cycle apparatuses. 

1. A fluid machine comprising: a closed casing; a rotation motor including a stator and a rotor, the rotation motor being disposed in the closed casing; a compressor for compressing a refrigerant and discharging it into the closed casing, the compressor being disposed in the closed casing; a power-recovery device for recovering power from the refrigerant by suctioning and discharging the refrigerant, the power-recovery device being disposed in the closed casing; a shaft extending vertically, the shaft being shared by the rotation motor, the compressor and the power-recovery device; and a sub-compressor for raising the pressure of the refrigerant and delivering the refrigerant to the compressor with the rotation of the shaft, the sub-compressor being disposed between the compressor and the power-recovery device.
 2. The fluid machine according to claim 1, wherein the compressor is located above the power-recovery device.
 3. The fluid machine according to claim 2, wherein an oil pool is formed in the bottom of the closed casing, the sub-compressor and the power-recovery device are disposed in the oil pool, and the compressor is located above the oil pool.
 4. The fluid machine according to claim 3, wherein the rotation motor is disposed between the compressor and the oil pool.
 5. The fluid machine according to claim 3 further comprising an oil pump for supplying oil in the oil pool to the compressor, wherein the oil pump is located above the sub-compressor.
 6. The fluid machine according to claim 5, wherein a space filled with either of the refrigerant immediately before being suctioned into the sub-compressor, or the refrigerant immediately after being discharged from the sub-compressor is provided between the sub-compressor and the oil pump.
 7. The fluid machine according to claim 1, wherein the compressor is a scroll type.
 8. The fluid machine according to any claim 1, wherein the sub-compressor and the power-recovery device each are a rotary type.
 9. The fluid machine according to claim 8, wherein the power-recovery device is a fluid pressure motor.
 10. The fluid machine according to claim 1, wherein the refrigerant is carbon dioxide.
 11. The fluid machine according to claim 1, wherein the ratio of the suction volume of the sub-compressor with respect to the suction volume of the compressor is 1.2 or less. 